Aggron’s Mega Stone, Aggronite, will be given to you by an NPC after you use Rock Smash to open the blocked path in Rusturf Tunnel that leads to Route 116.
But you’ll need to at least have the third Gym Badge from Wattson to do this, since you will need that badge to be able to use Rock Smash outside of battle.
Aggronite Location (Step-by-Step)
Rusturf Tunnel is a tunnel that connects Route 116 and Verdanturf Town. When you first have access to Route 116, the Rusturf Tunnel path leading to Verdanturf Town is blocked by boulders that are only breakable by HM06 Rock Smash.
You can obtain HM06 from Wally’s Uncle after you beat Wally in a battle in front of the Mauville City Gym.
However, you won’t be able to use Rock Smash outside of battle until you’ve obtained the Dynamo Badge from Wattson, the third Gym Leader.
After you obtain the third Gym Badge, make your way to Rusturf Tunnel. The fastest way there is from Verdanturf Town.
Here’s how you’ll get there and get your Aggronite:
Step 1: From Verdanturf Town’s Pokémon Center, start heading west.
Step 2: Head inside Rusturf Tunnel’s entrance, directly next to the Poké Mart.
Step 3: Follow the path heading north.
Step 4: As you approach the trainer on the left, she will ask you to break the boulders blocking the path using Rock Smash.
Step 5: After you break the boulders, the two of them will be reunited. Her boyfriend will give you the Aggronite as a token of gratitude.
How Aggronite Works
Mega Stones like the Aggronite are held items that allow certain Pokémon to Mega Evolve, granting them a massive boost to their base stats.
Some Pokémon also change types upon Mega Evolving.
Mega Aggron loses its Rock typing, becoming a pure Steel-type Pokémon.
And most Mega Evolutions also change the Pokémon’s ability, which lasts until the battle concludes. When Aggron Mega Evolves into Mega Aggron, it changes its ability to Filter, which reduces damage from super effective moves by 25%.
Boasting a massive Defense stat of 230 and a solid defensive typing, Mega Aggron is an excellent answer to any physical sweeper.
Its base Attack is very high as well for a defensive Pokémon. However, its HP and Special Defense stats are quite mediocre, limiting its effectiveness as a tank.
As for moves, Heavy Slam is Mega Aggron’s Same-Type Attack Bonus (STAB) move of choice. Its substantial weight makes Heavy Slam almost always have its maximum base power of 120.